An automatic transmission for a motor vehicle is normally designed as a stepped variable transmission, which is operated in auxiliary mode, wherein idler gears and fixed gears on at least one common transmission input shaft as well as on one transmission common output shaft are present and are at least pairwise meshed with one another. For the realization of a specific transmission gear, an idler gear is rotationally fixed on a common transmission shaft by way of a shifting or sliding collar so that torque transfer from a fixed gear to an idler gear can take place. The sliding collar, in this situation, is rotationally fixed as well as axially slidable along the common shaft and, different from a manually shiftable transmission, is energized by way of an actuator apparatus, i.e., a servo motor, which actuator apparatus itself is under the control of a transmission control center. As is well known, such an actuator apparatus can be designed to be energized by hydraulic, pneumatic or electrical power. The control of this type of actuator apparatus is executed with the aid of a program fed by input generated by strategically placed sensors, which signal directly to the control equipment.
In practice, such automatic transmissions have received, in a fully deserved manner, high claims for their control and regulation systems, since these both exhibit and enable a lengthy operational life; provide excellent shifting comfort at a low noise level, and function with short gear change times as well as quick availability when the vehicle has been put into operation.
These favorable requirements subject the control of the transmission, at least in part, to conflicting demands. As an example, the demand for short shifting times leads to comparatively high activation speeds of the actuator apparatus for the sliding collars which, in turn, brings about excessive velocities at a moment of gear contact between idler and fixed gears. Since a sliding collar is usually energized by an actuator apparatus, these two components are bound together by shifting rods and shifting forks, which increases the movable weight of the collar and thereby increases the kinetic energy of the movable parts.
The inevitable result includes comparably high noise levels, which arise from the impact of the respective toothing of the idler gear and the sliding collar and further, understandably, has an influence on the operational life of such a shifting apparatus, which must be ruggedly designed. This leads, in turn, to a high transmission weight and/or at least to increased cost of manufacture.
In order to meet the above stated problem, DE 197 56 637 A1 and DE 197 56 639 A1 propose a shifting apparatus, which has a supported aid for, as before, a multi-stage, stepped, variable transmission of auxiliary construction. This shifting apparatus includes valves and shifting cylinders, wherein pistons are provided which can be displaced by a fluid. In addition, shifting elements are provided wherein, in each shifting group, components of the transmission can be connected to allow torque transfer. This shifting apparatus is also characterized in, that for each shifting group, a provision is made in which the valve, shifting cylinder, piston and shifting element are assembled in one unit. Due to this combined construction, the otherwise customary connection elements between a shifting fork and an actuator apparatus can be eliminated. This elimination of the momentum masses allows that the reaction time is reduced between first, the signal, which releases a gearshift; second, the execution of this shift. Also connected thereto is a reduction of the kinetic energy which is to be brought into the system.
In this combination, the valves are designed as 2/2-way valves and are reactive to changes in pulsed signals. This allows that, during the carrying out of the shifting procedure, a mutual compensation between the force and time of shifting can be undertaken so that severe mechanical noise originating in impacts of toothing between the idler and the sliding collar can be avoided. The area of the problem lies in an actual control of the 2/2-way valves, especially in the case of tooth-to-tooth positioning of the interior toothing of the sliding collar and the complementary toothing of the idler during shifting. The noise also occurs in the case of the collar and idler gears when they release from one another with subsequent through-shifting.
An additional, more conventional shifting apparatus for an automatic transmission is disclosed by DE 102 34 357 A1, wherein even a case of operation is satisfactorily solved in that here tooth-to-tooth positioning is fostered between the inner toothing of the sliding collar and the complementary toothing of the idler. To accomplish this, a springlike, elastic activation means is provided for the sliding collar, which is also a shifting collar whereby, from a single actuator apparatus, the entire predetermined travel for the sliding collar results from the placement of a shifting rod between the elastic actuator apparatus and the sliding collar so that, now with an exact mutual tooth positioning between the collar and the idler gears, noisy mechanical gear engagement is excluded. If the principal shaft of the transmission or a selected gear is rotated, then the reaction must be a spring force supported continuation of the shifting of the selected gear, wherein one spring releases the operative force of the actuator apparatus, which force was not previously converted into a specified control direction. The disadvantage of this shifting apparatus is both the impacting of the respective teeth of the sliding collar and the idler gear and also disturbing shifting noises can be noticed during through-shifting because of the contact of the teeth.
Finally, in DE 196 10 827 A1 a procedure is known for the evaluation of gear tooth noises, especially in the case of transmissions, wherein the manufacture of low-noise tooth-pairs can be advantageously carried out. For the evaluation of the noise of toothing, the speed of rotation of the gear under investigation is measured, and noise attributable to the toothing is picked up by a microphone and both signals are input into a Fast Fourier Transform Analyzer (hereinafter FFT). The FFT analyzer presents an output signal dependent upon the speed of rotation of the gear and valid for a preselected gearsetting.